1. Field of the Invention
The present invention relates generally to machining methods employing oblique workpiece spindle and with high precision, and more particularly to a machining method employing oblique workpiece spindle used in super precise machining.
2. Discussion of the Related Art
Molds for forming precise products such as lenses usually have high precision, small size, and small surface roughness etc. A working surface of the mold is usually a curved surface such as a concave spherical surface. Referring to FIG. 4, in a typical method, a grinding wheel 12 is used to grind a mold 14 so as to obtain a smooth working surface. The grinding wheel 12 is disk-shaped. During a machining process, the grinding wheel 12 rotates and moves along a path parallel to a predetermined surface of the mold 14. Shown in FIG. 4, the mold 14 has a small size as described above and the grinding wheel 12 is further smaller than the mold 14. Thus a diameter of the grinding wheel 12 should be very small. However, the grinding wheel 12 with the small diameter has low strength and rigidity. Thus, a precision of the mold 14 will be reduced due to deformation of the grinding wheel 12 when the grinding wheel 12 rotates.
In order to solve the above described problem, another machining method is provided. Referring to FIG. 5, a mold 22 is mounted on a workpiece spindle (not shown), and the workpiece spindle rotates in a Z-axis. A tool 24 is mounted on a tool spindle (not shown) rotating in a T-axis. An angle defined by the Z-axis relative to the T-axis is 45 degrees. That is, the T-axis is oblique relative to the Z-axis. The tool 24 is cylinder-shaped, and the tool 24 machines the mold 22 with a bottom edge thereof. Simultaneously, the tool 24 moves along directions parallel to a Y-axis and the Z-axis. Usually, a size of the tool 24 is relative large. So the tool 24 has a relative high strength and rigidity. However, the tool 24 and the tool spindle are oblique relative to the Z-axis. Thus, a component force of gravity of the tool 24 and tool spindle, in a direction perpendicular to the T-axis, causes shaking of the tool spindle. A machining precision is reduced because of the shaking of the tool spindle. In addition, an expensive, special tool spindle is employed in this method.
Therefore, a new machining method which has a high precision is desired.